1. Technical Field
Various embodiments of the present invention relate to a circuit device, an oscillator, an electronic apparatus, and a vehicle.
2. Related Art
In the related art, there is an oscillator such as an oven controlled crystal oscillator (OCXO) or a temperature compensated crystal oscillator (TCXO). For example, the OCXO is used as a reference signal source in a base station, a network router, a measurement apparatus, and the like.
High frequency stability is required in an oscillator such as the OCXO or the TCXO. However, a secular change called aging occurs in an oscillation frequency of an oscillator, and thus the oscillation frequency varies over time. For example, regarding the related art of reducing a variation in an oscillation frequency in a case where a reference signal such as a GPS signal cannot be received, and thus a so-called hold-over state occurs, there is a technique disclosed in JP-A-2015-82815. In this related art, there are provided a storage which stores correspondence relationship information (aging characteristic data) between a correction value of a control voltage for an oscillation frequency and the elapsed time, and an elapsed time measurer. In a case where a hold-over state is detected, aging correction is performed on the basis of the correspondence relationship information between a correction value and the elapsed time stored in the storage, and the elapsed time measured by the elapsed time measurer.
In a base station, a network router, a measurement apparatus, a phase locked loop (PLL) is configured to include an oscillator such as an OCXO or a TCXO, and an oscillation frequency of the oscillator is locked with a GPS signal or the like as a reference signal. In this case, for example, a user having knowhow on detection of a hold-over state, or switching from locking with the reference signal to a hold-over mode provides a phase comparator or a hold-over detection circuit outside an oscillator (a circuit device and a resonator), forms a PLL by using the oscillator, and can thus obtain a configuration most suitable for a system by performing control or the like based on the knowhow. On the other hand, in a case of a user who wants to cheaply obtain a synchronization clock of a small base station or the like, it is desirable to obtain a synchronization clock at low cost without forming a PLL outside an oscillator. As mentioned above, it is desirable to cope with various applications such as a method of forming a PLL or a method of generating a hold-over signal.